Java/Network Protocol/HttpURLConnection

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Available Port Finder

   <source lang="java">

/* 

*  Licensed to the Apache Software Foundation (ASF) under one
*  or more contributor license agreements.  See the NOTICE file
*  distributed with this work for additional information
*  regarding copyright ownership.  The ASF licenses this file
*  to you under the Apache License, Version 2.0 (the
*  "License"); you may not use this file except in compliance
*  with the License.  You may obtain a copy of the License at
*
*    http://www.apache.org/licenses/LICENSE-2.0
*
*  Unless required by applicable law or agreed to in writing,
*  software distributed under the License is distributed on an
*  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
*  KIND, either express or implied.  See the License for the
*  specific language governing permissions and limitations
*  under the License.
*
*/

import java.io.IOException; import java.net.DatagramSocket; import java.net.ServerSocket; import java.util.NoSuchElementException; import java.util.Set; import java.util.TreeSet; /** 

* Finds currently available server ports.
*
* @author The Apache MINA Project (dev@mina.apache.org)
* @version $Rev: 576217 $
* @see 
*/

public class AvailablePortFinder { 

   /**
    * The minimum number of server port number.
    */
   public static final int MIN_PORT_NUMBER = 1;
   /**
    * The maximum number of server port number.
    */
   public static final int MAX_PORT_NUMBER = 49151;
   /**
    * Creates a new instance.
    */
   private AvailablePortFinder() {
   }
   /**
    * Returns the {@link Set} of currently available port numbers
    * ({@link Integer}).  This method is identical to
    * getAvailablePorts(MIN_PORT_NUMBER, MAX_PORT_NUMBER).
    *
    * WARNING: this can take a very long time.
    */
   public static Set<Integer> getAvailablePorts() {
       return getAvailablePorts(MIN_PORT_NUMBER, MAX_PORT_NUMBER);
   }
   /**
    * Gets the next available port starting at the lowest port number.
    *
    * @throws NoSuchElementException if there are no ports available
    */
   public static int getNextAvailable() {
       return getNextAvailable(MIN_PORT_NUMBER);
   }
   /**
    * Gets the next available port starting at a port.
    *
    * @param fromPort the port to scan for availability
    * @throws NoSuchElementException if there are no ports available
    */
   public static int getNextAvailable(int fromPort) {
       if (fromPort < MIN_PORT_NUMBER || fromPort > MAX_PORT_NUMBER) {
           throw new IllegalArgumentException("Invalid start port: "
                   + fromPort);
       }
       for (int i = fromPort; i <= MAX_PORT_NUMBER; i++) {
           if (available(i)) {
               return i;
           }
       }
       throw new NoSuchElementException("Could not find an available port "
               + "above " + fromPort);
   }
   /**
    * Checks to see if a specific port is available.
    *
    * @param port the port to check for availability
    */
   public static boolean available(int port) {
       if (port < MIN_PORT_NUMBER || port > MAX_PORT_NUMBER) {
           throw new IllegalArgumentException("Invalid start port: " + port);
       }
       ServerSocket ss = null;
       DatagramSocket ds = null;
       try {
           ss = new ServerSocket(port);
           ss.setReuseAddress(true);
           ds = new DatagramSocket(port);
           ds.setReuseAddress(true);
           return true;
       } catch (IOException e) {
       } finally {
           if (ds != null) {
               ds.close();
           }
           if (ss != null) {
               try {
                   ss.close();
               } catch (IOException e) {
                   /* should not be thrown */
               }
           }
       }
       return false;
   }
   /**
    * Returns the {@link Set} of currently avaliable port numbers ({@link Integer})
    * between the specified port range.
    *
    * @throws IllegalArgumentException if port range is not between
    * {@link #MIN_PORT_NUMBER} and {@link #MAX_PORT_NUMBER} or
    * fromPort if greater than toPort.
    */
   public static Set<Integer> getAvailablePorts(int fromPort, int toPort) {
       if (fromPort < MIN_PORT_NUMBER || toPort > MAX_PORT_NUMBER
               || fromPort > toPort) {
           throw new IllegalArgumentException("Invalid port range: "
                   + fromPort + " ~ " + toPort);
       }
       Set<Integer> result = new TreeSet<Integer>();
       for (int i = fromPort; i <= toPort; i++) {
           ServerSocket s = null;
           try {
               s = new ServerSocket(i);
               result.add(new Integer(i));
           } catch (IOException e) {
           } finally {
               if (s != null) {
                   try {
                       s.close();
                   } catch (IOException e) {
                       /* should not be thrown */
                   }
               }
           }
       }
       return result;
   }

} 

 </source>



A Web Page Source Viewer

   <source lang="java">

import java.awt.BorderLayout; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.io.BufferedInputStream; import java.io.InputStream; import java.io.InputStreamReader; import java.io.Reader; import java.net.HttpURLConnection; import java.net.URL; import javax.swing.JButton; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.JTextArea; public class Main extends JFrame { 

 JButton go = new JButton("Get Source");
 JTextArea codeArea = new JTextArea();
 public Main() {
   JPanel inputPanel = new JPanel(new BorderLayout(3, 3));
   go.addActionListener(new ActionListener() {
     public void actionPerformed(ActionEvent e) {
       try {
         URL pageURL = new URL("http://www.google.ru");
         HttpURLConnection urlConnection = (HttpURLConnection) pageURL.openConnection();
         int respCode = urlConnection.getResponseCode();
         String response = urlConnection.getResponseMessage();
         codeArea.setText("HTTP/1.x " + respCode + " " + response + "\n");
         int count = 1;
         while (true) {
           String header = urlConnection.getHeaderField(count);
           String key = urlConnection.getHeaderFieldKey(count);
           if (header == null || key == null) {
             break;
           }
           codeArea.append(urlConnection.getHeaderFieldKey(count) + ": " + header + "\n");
           count++;
         }
         InputStream in = new BufferedInputStream(urlConnection.getInputStream());
         Reader r = new InputStreamReader(in);
         int c;
         while ((c = r.read()) != -1) {
           codeArea.append(String.valueOf((char) c));
         }
         codeArea.setCaretPosition(1);
       } catch (Exception ee) {
       }
     }
   });
   inputPanel.add(BorderLayout.EAST, go);
   JScrollPane codeScroller = new JScrollPane(codeArea);
   add(BorderLayout.NORTH, inputPanel);
   add(BorderLayout.CENTER, codeScroller);
   this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   this.setSize(700, 500);
   this.setVisible(true);
 }
 public static void main(String[] args) {
   JFrame webPageSourceViewer = new Main();
 }

} 



 </source>



Check if a page exists

   <source lang="java">

import java.net.HttpURLConnection; import java.net.URL; public class Main { 

 public static void main(String[] argv) throws Exception {
   HttpURLConnection.setFollowRedirects(false);
   HttpURLConnection con = (HttpURLConnection) new URL("http://www.google.coom").openConnection();
   con.setRequestMethod("HEAD");
   System.out.println(con.getResponseCode() == HttpURLConnection.HTTP_OK);
 }

} 



 </source>



Connect through a Proxy

   <source lang="java">

import java.io.DataInputStream; import java.io.FileOutputStream; import java.net.HttpURLConnection; import java.net.URL; import java.util.Properties; import sun.misc.BASE64Encoder; public class Main { 

 public static void main(String[] argv) throws Exception {
   byte[] b = new byte[1];
   Properties systemSettings = System.getProperties();
   systemSettings.put("http.proxyHost", "proxy.mydomain.local");
   systemSettings.put("http.proxyPort", "80");
   URL u = new URL("http://www.google.ru");
   HttpURLConnection con = (HttpURLConnection) u.openConnection();
   BASE64Encoder encoder = new BASE64Encoder();
   String encodedUserPwd = encoder.encode("mydomain\\MYUSER:MYPASSWORD".getBytes());
   con.setRequestProperty("Proxy-Authorization", "Basic " + encodedUserPwd);
   DataInputStream di = new DataInputStream(con.getInputStream());
   while (-1 != di.read(b, 0, 1)) {
     System.out.print(new String(b));
   }
 }

} 



 </source>



Converting x-www-form-urlencoded Data

   <source lang="java">

import java.net.URLEncoder; public class Main { 

 public static void main(String[] argv) throws Exception {
    String line = URLEncoder.encode("name1", "UTF-8") + "=" + URLEncoder.encode("value1", "UTF-8");
 }

} 



 </source>



Display header information

   <source lang="java">

import java.net.HttpURLConnection; import java.net.URL; import java.util.List; import java.util.Map; import java.util.Set; public class Main{ 

 public static void main(String args[]) throws Exception {
   URL url = new URL("http://www.google.ru");
   HttpURLConnection httpCon = (HttpURLConnection) url.openConnection();
   Map<String, List<String>> hdrs = httpCon.getHeaderFields();
   Set<String> hdrKeys = hdrs.keySet();
   for (String k : hdrKeys)
     System.out.println("Key: " + k + "  Value: " + hdrs.get(k));
}

} 



 </source>



Display request method

   <source lang="java">

import java.net.HttpURLConnection; import java.net.URL; import java.util.Date; public class Main{ 

 public static void main(String args[]) throws Exception {
   URL url = new URL("http://www.google.ru");
   HttpURLConnection httpCon = (HttpURLConnection) url.openConnection();
   System.out.println("Request method is " + httpCon.getRequestMethod());
}

} 



 </source>



Display response message

   <source lang="java">

import java.net.HttpURLConnection; import java.net.URL; import java.util.Date; public class Main{ 

 public static void main(String args[]) throws Exception {
   URL url = new URL("http://www.google.ru");
   HttpURLConnection httpCon = (HttpURLConnection) url.openConnection();
   System.out.println("Response Message is " + httpCon.getResponseMessage());
}

} 



 </source>



Download and display the content

   <source lang="java">

import java.io.InputStream; import java.net.HttpURLConnection; import java.net.URL; public class Main { 

 public static void main(String args[]) throws Exception {
   URL url = new URL("http://www.google.ru");
   HttpURLConnection httpCon = (HttpURLConnection) url.openConnection();
   InputStream inStrm = httpCon.getInputStream();
   System.out.println("\nContent at " + url);
   int ch;
   while (((ch = inStrm.read()) != -1))
     System.out.print((char) ch);
   inStrm.close();
 }

} 



 </source>



Get response code

   <source lang="java">

import java.net.HttpURLConnection; import java.net.URL; import java.util.Date; public class Main{ 

 public static void main(String args[]) throws Exception {
   URL url = new URL("http://www.google.ru");
   HttpURLConnection httpCon = (HttpURLConnection) url.openConnection();

   System.out.println("Response code is " + httpCon.getResponseCode());
}

} 



 </source>



Get the date of a url connection

   <source lang="java">

import java.net.HttpURLConnection; import java.net.URL; import java.util.Date; public class Main{ 

 public static void main(String args[]) throws Exception {
   URL url = new URL("http://www.google.ru");
   HttpURLConnection httpCon = (HttpURLConnection) url.openConnection();
   long date = httpCon.getDate();
   if (date == 0)
     System.out.println("No date information.");
   else
     System.out.println("Date: " + new Date(date));
}

} 



 </source>



Get the document expiration date

   <source lang="java">

import java.net.HttpURLConnection; import java.net.URL; import java.util.Date; public class Main{ 

 public static void main(String args[]) throws Exception {
   URL url = new URL("http://www.google.ru");
   HttpURLConnection httpCon = (HttpURLConnection) url.openConnection();
   long date = httpCon.getExpiration();
   if (date == 0)
     System.out.println("No expiration information.");
   else
     System.out.println("Expires: " + new Date(date));
}

} 



 </source>



Get the document Last-modified date

   <source lang="java">

import java.net.HttpURLConnection; import java.net.URL; import java.util.Date; public class Main{ 

 public static void main(String args[]) throws Exception {
   URL url = new URL("http://www.google.ru");
   HttpURLConnection httpCon = (HttpURLConnection) url.openConnection();
   long date = httpCon.getLastModified();
   if (date == 0)
     System.out.println("No last-modified information.");
   else
     System.out.println("Last-Modified: " + new Date(date));
}

} 



 </source>



Getting the Cookies from an HTTP Connection

   <source lang="java">

import java.net.URL; import java.net.URLConnection; public class Main { 

 public static void main(String[] argv) throws Exception {
   URL url = new URL("http://hostname:80");
   URLConnection conn = url.openConnection();
   for (int i = 0;; i++) {
     String headerName = conn.getHeaderFieldKey(i);
     String headerValue = conn.getHeaderField(i);
     if (headerName == null && headerValue == null) {
       break;
     }
     if ("Set-Cookie".equalsIgnoreCase(headerName)) {
       String[] fields = headerValue.split(";\\s*");
       for (int j = 1; j < fields.length; j++) {
         if ("secure".equalsIgnoreCase(fields[j])) {
           System.out.println("secure=true");
         } else if (fields[j].indexOf("=") > 0) {
           String[] f = fields[j].split("=");
           if ("expires".equalsIgnoreCase(f[0])) {
             System.out.println("expires"+ f[1]);
           } else if ("domain".equalsIgnoreCase(f[0])) {
             System.out.println("domain"+ f[1]);
           } else if ("path".equalsIgnoreCase(f[0])) {
             System.out.println("path"+ f[1]);
           }
         }
       }
     }
   }
 }

} 



 </source>



Getting the Response Headers from an HTTP Connection

   <source lang="java">

import java.net.URL; import java.net.URLConnection; public class Main { 

 public static void main(String[] argv) throws Exception {
   URL url = new URL("http://hostname:80");
   URLConnection conn = url.openConnection();
   for (int i = 0;; i++) {
     String headerName = conn.getHeaderFieldKey(i);
     String headerValue = conn.getHeaderField(i);
     System.out.println(headerName);
     System.out.println(headerValue);
     if (headerName == null && headerValue == null) {
       System.out.println("No more headers");
       break;
     }
   }
 }

} 



 </source>



Grabbing a page using socket

   <source lang="java">

import java.io.BufferedReader; import java.io.BufferedWriter; import java.io.FileWriter; import java.io.InputStreamReader; import java.io.OutputStreamWriter; import java.net.Socket; import java.net.URL; public class Main { 

 public static void main(String[] args) throws Exception {
   String pageAddr = "http://www.google.ru/index.htm";
   URL url = new URL(pageAddr);
   String websiteAddress = url.getHost();
   String file = url.getFile();
   Socket clientSocket = new Socket(websiteAddress, 80);
   BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket
       .getInputStream()));
   OutputStreamWriter outWriter = new OutputStreamWriter(clientSocket.getOutputStream());
   outWriter.write("GET " + file + " HTTP/1.0\r\n\n");
   outWriter.flush();
   BufferedWriter out = new BufferedWriter(new FileWriter(file));
   boolean more = true;
   String input;
   while (more) {
     input = inFromServer.readLine();
     if (input == null)
       more = false;
     else {
       out.write(input);
     }
   }
   out.close();
   clientSocket.close();
 }

} 


 </source>



Http connection Utilities

   <source lang="java">

/********************************************************************************** 

*
* Copyright (c) 2003, 2004 The Regents of the University of Michigan, Trustees of Indiana University,
*                  Board of Trustees of the Leland Stanford, Jr., University, and The MIT Corporation
*
* Licensed under the Educational Community License Version 1.0 (the "License");
* By obtaining, using and/or copying this Original Work, you agree that you have read,
* understand, and will comply with the terms and conditions of the Educational Community License.
* You may obtain a copy of the License at:
*
*      http://cvs.sakaiproject.org/licenses/license_1_0.html
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
* INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
* AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
* DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*
**********************************************************************************/

import java.io.UnsupportedEncodingException; import java.net.MalformedURLException; import java.net.URL; import java.net.URLEncoder; import java.util.Enumeration; import java.util.HashMap; import java.util.Map; import javax.servlet.http.HttpServletRequest; /** 

* HTTP utilites
*/

public class HttpTransactionUtils { 

 private HttpTransactionUtils() {
 }
 /**
  * Default HTTP character set
  */
 public static final String DEFAULTCS = "ISO-8859-1";
 /*
  * Parameter handling
  */
 /**
  * Format one HTTP parameter
  * 
  * @param name
  *          Parameter name
  * @param value
  *          Parameter value (URLEncoded using default chracter set)
  * @return Parameter text (ampersand+name=url-encoded-value)
  */
 public static String formatParameter(String name, String value) {
   return formatParameter(name, value, "&", DEFAULTCS);
 }
 /**
  * Format one HTTP parameter
  * 
  * @param name
  *          Parameter name
  * @param value
  *          Parameter value (will be URLEncoded)
  * @param separator
  *          Character to separate parameters
  * @param cs
  *          Character set specification (utf-8, etc)
  * @return Parameter text (separator+name=url-encoded-value)
  */
 public static String formatParameter(String name, String value, String separator, String cs) {
   StringBuilder parameter = new StringBuilder();
   parameter.append(separator);
   parameter.append(name);
   parameter.append("=");
   try {
     parameter.append(URLEncoder.encode(value, cs));
   } catch (UnsupportedEncodingException exception) {
     throw new IllegalArgumentException("Invalid character set: \"" + cs + "\"");
   }
   return parameter.toString();
 }
 /*
  * HTTP status values
  */
 /**
  * Informational status?
  * 
  * @return true if so
  */
 public static boolean isHttpInfo(int status) {
   return ((status / 100) == 1);
 }
 /**
  * HTTP redirect?
  * 
  * @return true if so
  */
 public static boolean isHttpRedirect(int status) {
   return ((status / 100) == 3);
 }
 /**
  * Success status?
  * 
  * @return true if so
  */
 public static boolean isHttpSuccess(int status) {
   return ((status / 100) == 2);
 }
 /**
  * Error in request?
  * 
  * @return true if so
  */
 public static boolean isHttpRequestError(int status) {
   return ((status / 100) == 4);
 }
 /**
  * Server error?
  * 
  * @return true if so
  */
 public static boolean isHttpServerError(int status) {
   return ((status / 100) == 5);
 }
 /**
  * General "did an error occur"?
  * 
  * @return true if so
  */
 public static boolean isHttpError(int status) {
   return isHttpRequestError(status) || isHttpServerError(status);
 }
 /**
  * Set up a simple Map of HTTP request parameters (assumes no duplicate names)
  * 
  * @param request
  *          HttpServletRequest object
  * @return Map of name=value pairs
  */
 public static Map getAttributesAsMap(HttpServletRequest request) {
   Enumeration enumeration = request.getParameterNames();
   HashMap map = new HashMap();
   while (enumeration.hasMoreElements()) {
     String name = (String) enumeration.nextElement();
     map.put(name, request.getParameter(name));
   }
   return map;
 }
 /**
  * Format a base URL string ( protocol://server[:port] )
  * 
  * @param url
  *          URL to format
  * @return URL string
  */
 public static String formatUrl(URL url) throws MalformedURLException {
   return formatUrl(url, false);
 }
 /**
  * Format a base URL string ( protocol://server[:port][/file-specification] )
  * 
  * @param url
  *          URL to format
  * @param preserveFile
  *          Keep the /directory/filename portion of the URL?
  * @return URL string
  */
 public static String formatUrl(URL url, boolean preserveFile) throws MalformedURLException {
   StringBuilder result;
   int port;
   result = new StringBuilder(url.getProtocol());
   result.append("://");
   result.append(url.getHost());
   if ((port = url.getPort()) != -1) {
     result.append(":");
     result.append(String.valueOf(port));
   }
   if (preserveFile) {
     String file = url.getFile();
     if (file != null) {
       result.append(file);
     }
   }
   return result.toString();
 }
 /**
  * Pull the server [and port] from a URL specification
  * 
  * @param url
  *          URL string
  * @return server[:port]
  */
 public static String getServer(String url) {
   String server = url;
   int protocol, slash;
   if ((protocol = server.indexOf("//")) != -1) {
     if ((slash = server.substring(protocol + 2).indexOf("/")) != -1) {
       server = server.substring(0, protocol + 2 + slash);
     }
   }
   return server;
 }
 /*
  * urlEncodeParameters(): URL component specifications
  */
 /**
  * protocol://server
  */
 public static final String SERVER = "server";
 /**
  * /file/specification
  */
 public static final String FILE = "file";
 /**
  * ?parameter1=value1&parameter2=value2
  */
 public static final String PARAMETERS = "parameters";
 /**
  * /file/specification?parameter1=value1&parameter2=value2
  */
 public static final String FILEANDPARAMS = "fileandparameters";
 /**
  * Fetch a component from a URL string
  * 
  * @param url
  *          URL String
  * @param component
  *          name (one of server, file, parameters, fileandparameters)
  * @return URL component string (null if none)
  */
 public static String getUrlComponent(String url, String component) throws MalformedURLException {
   String file;
   int index;
   if (component.equalsIgnoreCase(SERVER)) {
     return getServer(url);
   }
   if (!component.equalsIgnoreCase(FILE) && !component.equalsIgnoreCase(PARAMETERS)
       && !component.equalsIgnoreCase(FILEANDPARAMS)) {
     throw new IllegalArgumentException(component);
   }
   file = new URL(url).getFile();
   if (file == null) {
     return null;
   }
   /*
    * Fetch file and parameters?
    */
   if (component.equalsIgnoreCase(FILEANDPARAMS)) {
     return file;
   }
   /*
    * File portion only?
    */
   index = file.indexOf("?");
   if (component.equalsIgnoreCase(FILE)) {
     switch (index) {
     case -1: // No parameters
       return file;
     case 0: // Only parameters (no file)
       return null;
     default:
       return file.substring(0, index);
     }
   }
   /*
    * Isolate parameters
    */
   return (index == -1) ? null : file.substring(index);
 }
 /**
  * URLEncode parameter names and values
  * 
  * @param original
  *          Original parameter list (?a=b&c=d)
  * @return Possibly encoded parameter list
  */
 public static String urlEncodeParameters(String original) {
   StringBuilder encoded = new StringBuilder();
   for (int i = 0; i < original.length(); i++) {
     String c = original.substring(i, i + 1);
     if (!c.equals("&") && !c.equals("=") && !c.equals("?")) {
       c = URLEncoder.encode(c);
     }
     encoded.append(c);
   }
   return encoded.toString();
 }
 /*
  * Test
  */
 public static void main(String[] args) throws Exception {
   String u = "http://example.ru/dir1/dir2/file.html?parm1=1&param2=2";
   System.out.println("Server: " + getUrlComponent(u, "server"));
   System.out.println("File: " + getUrlComponent(u, "file"));
   System.out.println("Parameters: " + getUrlComponent(u, "parameters"));
   System.out.println("File & Parameters: " + getUrlComponent(u, "fileandparameters"));
   System.out.println("Bad: " + getUrlComponent(u, "bad"));
 }

} 

 </source>



Http Header Helper

   <source lang="java">

/** 

* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/

import java.nio.charset.Charset; import java.nio.charset.IllegalCharsetNameException; import java.nio.charset.UnsupportedCharsetException; import java.util.HashMap; import java.util.List; import java.util.Map; import java.util.concurrent.ConcurrentHashMap; public final class HttpHeaderHelper { 

   public static final String ACCEPT_ENCODING = "Accept-Encoding";
   public static final String CONTENT_TYPE = "Content-Type";
   public static final String CONTENT_ID = "Content-ID";
   public static final String CONTENT_ENCODING = "Content-Encoding";
   public static final String CONTENT_TRANSFER_ENCODING = "Content-Transfer-Encoding";
   public static final String COOKIE = "Cookie";
   public static final String TRANSFER_ENCODING = "Transfer-Encoding";
   public static final String CHUNKED = "chunked";
   public static final String CONNECTION = "Connection";
   public static final String CLOSE = "close";
   public static final String AUTHORIZATION = "Authorization";
   private static final Charset UTF8 = Charset.forName("utf-8"); 
   
   private static Map<String, String> internalHeaders = new HashMap<String, String>();
   private static Map<String, String> encodings = new ConcurrentHashMap<String, String>();
   
   static {
       internalHeaders.put("Accept-Encoding", "accept-encoding");
       internalHeaders.put("Content-Encoding", "content-encoding");
       internalHeaders.put("Content-Type", "content-type");
       internalHeaders.put("Content-ID", "content-id");
       internalHeaders.put("Content-Transfer-Encoding", "content-transfer-encoding"); 
       internalHeaders.put("Transfer-Encoding", "transfer-encoding");
       internalHeaders.put("Connection", "connection");
       internalHeaders.put("authorization", "Authorization");
       internalHeaders.put("soapaction", "SOAPAction");
       internalHeaders.put("accept", "Accept");
   }
   
   private HttpHeaderHelper() {
       
   }
   
   public static List getHeader(Map<String, List<String>> headerMap, String key) {
       return headerMap.get(getHeaderKey(key));
   }
   
   public static String getHeaderKey(String key) {
       if (internalHeaders.containsKey(key)) {
           return internalHeaders.get(key);
       } else {
           return key;
       }
   }
   
   //helper to map the charsets that various things send in the http Content-Type header 
   //into something that is actually supported by Java and the Stax parsers and such.
   public static String mapCharset(String enc) {
       if (enc == null) {
           return UTF8.name();
       }
       //older versions of tomcat don"t properly parse ContentType headers with stuff
       //after charset="UTF-8"
       int idx = enc.indexOf(";");
       if (idx != -1) {
           enc = enc.substring(0, idx);
       }
       // Charsets can be quoted. But it"s quite certain that they can"t have escaped quoted or
       // anything like that.
       enc = enc.replace("\"", "").trim();
       enc = enc.replace(""", "");
       if ("".equals(enc)) {
           return UTF8.name();
       }
       String newenc = encodings.get(enc);
       if (newenc == null) {
           try {
               newenc = Charset.forName(enc).name();
           } catch (IllegalCharsetNameException icne) {
               return null;
           } catch (UnsupportedCharsetException uce) {
               return null;
           }
           encodings.put(enc, newenc);
       }
       return newenc;
   }

} 


 </source>



java.net.Authenticator can be used to send the credentials when needed

   <source lang="java">

import java.io.DataInputStream; import java.net.Authenticator; import java.net.HttpURLConnection; import java.net.PasswordAuthentication; import java.net.URL; import java.util.Properties; public class Main { 

 public static void main(String[] argv) throws Exception {
   byte[] b = new byte[1];
   Properties systemSettings = System.getProperties();
   systemSettings.put("http.proxyHost", "proxy.mydomain.local");
   systemSettings.put("http.proxyPort", "80");
   Authenticator.setDefault(new Authenticator() {
     protected PasswordAuthentication getPasswordAuthentication() {
       return new PasswordAuthentication("mydomain\\username", "password".toCharArray());
     }
   });
   URL u = new URL("http://www.google.ru");
   HttpURLConnection con = (HttpURLConnection) u.openConnection();
   DataInputStream di = new DataInputStream(con.getInputStream());
   while (-1 != di.read(b, 0, 1)) {
     System.out.print(new String(b));
   }
 }

} 



 </source>



Preventing Automatic Redirects in a HTTP Connection

   <source lang="java">

import java.net.HttpURLConnection; import java.net.URL; import java.net.URLConnection; public class Main { 

 public static void main(String[] argv) throws Exception {
   HttpURLConnection.setFollowRedirects(false);
   URL url = new URL("http://hostname:80");
   URLConnection conn = url.openConnection();
   HttpURLConnection httpConn = (HttpURLConnection) conn;
   httpConn.setInstanceFollowRedirects(false);
   conn.connect();
 }

} 



 </source>



Reading from a URLConnection

   <source lang="java">

import java.io.BufferedReader; import java.io.InputStreamReader; import java.net.URL; import java.net.URLConnection; public class Main { 

 public static void main(String[] args) throws Exception {
   URL yahoo = new URL("http://www.yahoo.ru/");
   URLConnection yc = yahoo.openConnection();
   BufferedReader in = new BufferedReader(new InputStreamReader(yc.getInputStream()));
   String inputLine;
   while ((inputLine = in.readLine()) != null)
     System.out.println(inputLine);
   in.close();
 }

} 



 </source>



Sending a Cookie to an HTTP Server

   <source lang="java">

import java.net.URL; import java.net.URLConnection; public class Main { 

 public static void main(String[] argv) throws Exception {
   URL url = new URL("http://hostname:80");
   URLConnection conn = url.openConnection();
   conn.setRequestProperty("Cookie", "name1=value1; name2=value2");
   conn.connect();
 }

} 



 </source>



Show the content length

   <source lang="java">

import java.net.HttpURLConnection; import java.net.URL; import java.util.Date; public class Main{ 

 public static void main(String args[]) throws Exception {
   URL url = new URL("http://www.google.ru");
   HttpURLConnection httpCon = (HttpURLConnection) url.openConnection();

   int len = httpCon.getContentLength();
   if (len == -1)
     System.out.println("Content length unavailable.");
   else
     System.out.println("Content-Length: " + len);
}

} 



 </source>



Show the content type

   <source lang="java">

import java.net.HttpURLConnection; import java.net.URL; import java.util.Date; public class Main{ 

 public static void main(String args[]) throws Exception {
   URL url = new URL("http://www.google.ru");
   HttpURLConnection httpCon = (HttpURLConnection) url.openConnection();

   System.out.println("Content-Type: " + httpCon.getContentType());
}

} 



 </source>



Use BufferedReader to read content from a URL

   <source lang="java">

import java.io.BufferedReader; import java.io.InputStreamReader; import java.net.HttpURLConnection; import java.net.URL; import java.net.URLConnection; public class Main { 

 public static void main(String[] argv) throws Exception {
   URL url = new URL("http://www.java.ru");
   URLConnection urlConnection = url.openConnection();
   HttpURLConnection connection = null;
   if (urlConnection instanceof HttpURLConnection) {
     connection = (HttpURLConnection) urlConnection;
   } else {
     System.out.println("Please enter an HTTP URL.");
     return;
   }
   BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
   String urlString = "";
   String current;
   while ((current = in.readLine()) != null) {
     urlString += current;
   }
   System.out.println(urlString);
 }

} 



 </source>
Источник — «http://jexp.ru/index.php?title=Java/Network_Protocol/HttpURLConnection&oldid=8893»